1. Field of the Invention
The present invention generally relates to a data recording apparatus, and more particularly to the data recording apparatus in which original data is modulated in accordance with a predetermined run length limitation rule and data obtained by modulating the original data is written on a recording medium.
Moreover, the present invention generally relates to a data reproducing apparatus, and more particularly to the data reproducing apparatus in which data is reproduced by using a Viterbi decoding algorithm from a reproduction signal that is based on a partial-response waveform obtained from the recording medium.
Furthermore, the present invention generally relates to a data recording/reproducing apparatus including each function of the data recording apparatus described above and the data reproducing apparatus.
2. Description of the Related Art
A magneto-optical disc as an example of the data recording/reproducing apparatus has been widely used in various fields to record or reproduce image information or to record or reproduce various coded data for a computer because of a large capacity, a lower price, a high reliability, and a like. As for the magneto-optical disc, it is desired to improve much larger capacity of storage, to record data at higher density, and to reproduce the data with high precision.
As a technology of recording and reproducing data with high precision, for example, one technology is proposed in that a record signal obtained by modulating data to be recorded to the partial-response waveform is recorded on the magneto-optical disc, and a most likelihood (ML) data is detected by a most likelihood data detector (for example, Viterbi detector) after sampling a reproduction signal from the magneto-optical disc at a predetermined period.
For example, the Viterbi detector is configured as shown in FIG. 1.
Referring to FIG. 1, the Viterbi detector includes a branch metric calculating unit (hereinafter, simply called BM) 101, an Add-Compare-Select unit (hereinafter, simply called ACS) 102, a path metric memory (hereinafter, simply called PMM) 103, and a path memory (hereinafter, simply called PM) 104.
In the Viterbi detector applied to a data read system of the magneto-optical-disc device, a sampling value yt of the reproduction signal from a magneto-optical disc is supplied to the BM 101, and the BM 101 calculates a branch metric value (hereinafter, simply called BM value) that is a difference of the sampling value yt and an expected value. The expected value is a value depending on the partial-response waveform used when data is recorded and is a value which the reproduction signal can originally be. The BM value is calculated for every expected value when one sampling value yt is supplied to the BM 101.
The ACS 102 adds the BM value mentioned above and a path metric value (hereinafter, simply called PM value) stored in the PMM 103 one clock before (Add), and compares every two PM values after the addition (Compare). Subsequently, as a result of the comparison described above, the ACS 102 selects the PM value being smaller as a new PM value (Select), and stores the selected PM value in the PMM 103. As a result of such this process, the PM value is a summation of the BM values. Selecting a certain PM value is equivalent to selecting a path of a state transition. That is, the ACS 102 always selects the path of the state transition with where the PM value becomes a minimum value.
Data (binary data) corresponding to the path selected are supplied to the PM 104 from the ACS 102. The PM 104 sequentially shifts data corresponding to each path selected. In this process, the data, which correspond to each path and are considered not to have been selected based on the succession of the state transition, are continuously eliminated. Consecutively, the PM 104 outputs the data corresponding to a surviving path as detected data.
As described above, record data is modulated to the record signal in accordance with the partial-response waveform, and the record signal is recorded on the magneto-optical disc. On the other hand, data, which are recorded on the magneto-optical disc at high density, are reproduced with high precision from the magneto-optical disc. Such a record/reproduction technique is called the technique of a partial response and most-likelihood detection (hereinafter, simply called PRML).
However, in the data recording/reproducing apparatus using the magneto-optical disc of the ISO (International Organization for Standardization) standard, a clock signal for synchronization is generated according to a so-called self-clocking technique. In the self-clocking technique, the clock signal is generated so as to actually synchronize with changes of the reproduction signal read from the magneto-optical disc. Accordingly, in order to avoid a state in that the reproduction signal has not changed for a long time, data to be recorded (hereinafter, called original data) are modulated in accordance with a predetermined run length limitation rule (for example, (1,7)RLL (Run Length Limitation) and data to be actually written on the magneto-optical disc are generated. Therefore, in the data to be actually written on the magneto-optical disc, a bit of the same value (“0” or “1”) does not continue more than a predetermined number.
When the record data is reproduced by the Viterbi detection based on the reproduction signal read from the magneto-optical disc recording data obtained by modulating the original data in accordance with the predetermined run length limitation rule, it is not required to consider any state transition that can not exist based on the predetermined run length limitation rule. Based on a limitation of possible state transitions (for example, called D-limitation), it is possible to simplify a process of the ACS 102.
In general, It is possible to include one or a plurality of parity bits for every predetermined bit number in the data written in the magneto-optical disc. In this case, the data is reproduced from the reproduction signal read from the magneto-optical disc, and the parity bits are checked for every predetermined bit number in the reproduction data. Thus, it is possible to check whether or not the reproduction data has an error.
In a case in which the original data is modulated in accordance with the predetermined run length limitation rule and data to be actually written in the magneto-optical disc are generated, there is a problem of how to insert the parity bits into the data.
For example, if data obtained as the record data by adding parity bits to the original data is modulated in accordance with the run length limitation rule in the read system, those parity bits do not become effective until the record data is reproduced by a demodulation corresponding to the modulation in accordance with the run length limitation rule. Thus, in a reproduction process by the Viterbi detection before the modulation described above, the parity bits cannot be used effectively.
Moreover, if the parity bits are added to the data obtained by modulating the original data in accordance with the predetermined run length limitation rule, the run length limitation rule is not followed for the data as a whole.
Thus, when the original data are modulated in accordance with the run length limitation rule and data to be written are generated, arrangements for how to add the parity bits are needed.
Furthermore, in order to relieve the edge shift by light modulation record, a data reproducing apparatus is proposed in that final data is obtained by synthesizing data reproduced in accordance with the ML technique from the sampling value obtained synchronizing with a leading edge (front edge) of the reproduction signal and data reproduced in accordance with the ML technique from the sampling value obtained synchronizing with the trailing edge (back edge) of the reproduction signal. This data reproducing apparatus requires two systems (a front edge processing system and a back edge processing system) for reproducing data from the reproduction signal. Therefore, it is desired to simplify the circuit configuration of the data reproducing apparatus as much as possible.